The present invention relates generally to heat dissipation and heat sensitive warning methods and apparatus to protect railway wheel set assemblies from severe thermal damages, to help detection of failed bearings and prevention of bearing failure related derailments. In particular, the present invention relates to method and apparatus for constant thermal indication and constant heat dissipation with heat pipes embedded within vehicle wheel set assemblies.
Overheated bearings on railroad vehicles are the results of either improper bearing mounting process or incipient bearing problems. Some overheated bearings have led to catastrophic failures and train derailments costing the North American railroads millions of dollars each year.
Among various methods proposed for timely detection of troubled bearings in order to replace them, wayside hot bearing detection systems using infrared sensors are representative of the state of the art and presently applied in high traffic areas.
Despite all the technical advancements of wayside hot box detectors, the occurrence of bearing burnoff related derailment remains at a constant rate over the past several years for freight cars and in the mean time costs are escalating for false alarm set-offs which result in unnecessary train stops. Moreover, it is found difficult to adapt the hot box detector to the inboard bearing type of wheel set which is used widely in passenger and transit trains.
The major operational problem of bearing burnoffs is associated with the facts that hot bearing detectors are typically spaced at 15 to 30 mile intervals, and a burnoff that can happen in seconds or minutes may occur between detectors. Unnecessary stops caused by false alarms of hot bearing detectors are believed related to brake heat radiation during drag braking on wheels. Up till now, no promising methods have been proposed to further improve the performance of the presently installed hot bearing detection systems to reduce simultaneously the risks of derailments and the number of false alarms.
Several bearing failure detection methods and devices using complete different approaches have been suggested, such as:
(1) wayside and on-board acoustic bearing detectors using bearing acoustic and vibration signatures to detect incipient bearing failure; (Advanced Roller Bearing Inspection Systems, G. B. Anderson et al, 12th International Wheelset congress, September 1998);
(2) on-board overheated bearing detecting systems such as wax motor activated electronic indicators within hollow cap screws or fusible material and spring activated visual indicators in axle centers (U.S. Pat. No. 4,119,284, Belmont, U.S Pat. No. 4812826, Kaufman, et al, and U.S. Pat. No. 5,633,628, Denny, et al).
However, none of them have found high degrees of acceptance by North American railways due to concerns on whether they are more effective or more reliable alternatives.
During normal operation, a certain amount of heat is generated inside bearings due to the friction among the moving components. The heat generated by a properly functioning bearing can be readily transferred to the atmosphere through the bearing itself and the surrounding components of the wheel set assembly such as the axle, the wheels and the bearing adapters with an adequate margin of safety. However, when the axle and bearings are in a failure mode, limited capacity of wheel set assembly to transfer heat due to relatively low thermal conductivity of carbon steel results in high bearing temperatures. Hot bearing detection systems are designed on the basis of different thermal signatures of normal and failing bearings.
The presently installed wayside hot box detectors are designed to detect the bearings which have progressed into the later stage of incipient failure phase by the rising temperature. Those hot box detectors rely on the measurement of infrared energy radiated from the exterior surface of bearing and axle assembly to determine the assembly""s interior temperature.
Due to relatively low thermal conductivity of carbon steel, a thermal gradient is developed between the overheated zone within the axle/bearing assembly and the scan envelope of the hot box detector on the outside surfaces of the wheel set assembly. The thermal gradient makes a notable negative impact on the detectability of hot box detectors. In virtue of the thermal gradient, a threshold temperature in the scan envelope much lower than failure indicative temperature inside bearing has to be set up to trigger the alarm in order to keep sufficient margin of safety. However, the dilemma is that lower threshold temperature may bring many false alarms ignited by other ambient heating effects, for example, drag braking on wheels.
Another deficiency of the present hot bearing detection systems is associated with the present setup of hot box detectors spaced at 15 or 30 mile intervals. With this set up, an overheated bearing that has not led to an immediate catastrophic failure can be picked up and removed from the service in time. However, in certain conditions, bearing failure can progress very fast and it reaches the final burnoff stage very quickly. A Tremendous amount of heat generated and accumulated in the rapidly progressed failure process leads to immediate decomposition of lubricant, severe degradation of bearing components and finally catastrophic derailment before the train reaches the next available hot box detector.
Accordingly, what is needed in the art is an improved method and apparatus to give constantly precise indication of interior temperatures of the bearing/axle assembly to the hot bearing detection systems and to provide the hot bearing detection system with sufficient time to pick up the overheated bearings by retarding the bearing failure progress through rapid heat dissipation.
One object of the present invention is to provide a method and apparatus for precise thermal indication of interior temperature of the bearing/axle assembly that will enable hot bearing detection systems to identify accurately overheated bearings without false alarms.
Another object of the present invention is to provide a rapid heat dissipation method and apparatus that is able to retard the bearing failure progress by fast cooling so as to give the detecting systems sufficient time to locate the failed bearings.
These objects of invention can be accomplished simultaneously by embedding heat pipes within the vehicle wheel set assembly that allows fast heat transfer:
(a) from the interior of the bearing and axle journal to heat dissipation areas either on surfaces of existing wheel set assembly components or on surfaces of additional cooling fins mounted on the wheel set assembly.
(b) from overheated zone inside the bearing and the axle where heat starts to build up, to thermal indication areas monitored by hot bearing detection systems or other types of thermal sensors.
Other objects and advantages of the present invention can become more apparent to those skilled in the art as the nature of the invention is better understood from the accompanying drawings and a detailed description.